Adenoid Cystic Carcinoma

• Adenoid cystic carcinoma (ACC):
  • Accounts for approximately 10% of all salivary gland neoplasms
  • This is the most common malignant disorder:
    • To arise in the submandibular, the sublingual, and the minor salivary glands
  • More than two thirds (65%) of them arise from the:
    • Minor salivary glands
  • ACC are most commonly located within:
    • The oral cavity (palate) followed by:
      • The nasal cavity and nasopharynx
  • They were considered the most common malignant salivary gland tumor to involve the palate:
    • But they are now outnumbered at this site:
      • Polymorphous low-grade adenocarcinoma
  • ACC arise more often in:
    • Women than in men
  • ACC tend to affect adults:
    • In their fifth through seventh decades of life
  • ACC often present as
    • An otherwise asymptomatic mass
• Its natural history demonstrates a paradox:
  • First:
    • Tumor growth is slow:
      • But its clinical course is unyielding and progressive
  • Second:
    • Operative intervention is usually possible:
      • But multiple local recurrences are the norm
  • Third:
    • Metastatic spread to regional lymph nodes is rare:
      • But distant spread to the lungs and bones is common:
        • 40% to 50% of the cases
  • Fourth:
    • 5-year survival rates are expectantly high:
      • But 10 to 20-year survival rates are dismally low [29]
• Tumor stage is considered the most reliable indicator of overall outcome:
  • But some authors have questioned the importance of histologic subtyping
• There is a strong positive correlation between site of origin and prognosis:
  • The more favorable outcome with major (relative to minor) salivary gland ACC:
    • Is attributed to the earlier discovery of the neoplasm at these more accessible locations
• ACC is not encapsulated or partially encapsulated:
  • Infiltrates the surrounding tissue:
    • The risk of local failure is:
      • Approximately 50% with surgery alone
• Histologically:
  • They have a basaloid epithelium clustered in nests in a hyaline stroma
  • ACC can be categorized into three growth patterns:
    • Cribriform pattern
    • Tubular pattern
    • Solid pattern
  • The most common histologic subtype is:
    • The cribriform type (44% of the cases)
      • Characterized by a “Swiss cheese” pattern of vacuolated areas
      • The prognosis for the cribriform subtype:
        • Is intermediate
  • The tubular subtype (35% of the cases):
    • Carries the best prognosis
    • Characterized by cords and nests of malignant cells
  • The solid subtype (21% of the cases):
    • Has the worst prognosis in terms of distant metastasis and long-term survival
    • Solid sheets of adenoid malignant cells characterize this subtype
• A sole feature of ACC is:
  • The propensity for perineural invasion:
    • 50% to 70% of the cases:
      • Even with early stage tumors
  • It can spread centripetally through the skull base and peripherally along both named and unnamed nerves
  • For this reason, adjuvant radiation that includes the anatomic course of the regional named nerves is often recommended
• Lymphatic spread is uncommon:
  • Consequently neck dissection or wide-field radiation to regional lymphatics:
    • Is rarely recommended
• Skip metastasis are known to occur despite clear surgical margins
• This malignancy is graded according to Szanto et al:
  • Cribriform or tubular (grade I)
  • Less than 30% solid (grade II)
  • Greater than 30% solid (grade III)
• In patients treated by similar modalities:
  • The cribriform and tubular variants of ACC demonstrated:
  • No difference in the rate of distant metastases and overall survival:
    • The cribriform variant demonstrated a:
      • Significantly worse prognosis in terms of local recurrence rate (up to 47%)

• References:
  • Spiro, R.H. and A.G. Huvos, Stage means more than grade in adenoid cystic carcinoma. American journal of surgery, 1992. 164: p.623-8.
  • Bradley, P.J., Adenoid cystic carcinoma of the head and neck:
    a review. Curr Opin Otolarngol Head Neck Surg. Vol. 12.
    2004: Lippincott Williams and Wilkins.
  • Martinez-Rodriguez, N., et al., Epidemiology and treatment
    of adenoid cystic carcinoma of the minor salivary glands: A
    meta-analytic study. Medicina oral, patologia oral y cirugia
    bucal, 2011.
  • Szanto, P.A., et al., Histologic grading of adenoid cystic
    carcinoma of the salivary glands. Cancer, 1984. 54(6): p.
    1062-9.
  • Kumar, P.P., et al., Intracranial skip metastasis from parotid
    and facial skin tumors: mechanism, diagnosis, and
    treatment. Journal of the National Medical Association, 85(5): p. 369-
  • Gnepp, D.R., Malignant mixed tumors of the salivary glands:
    a review. Pathology annual, 1993. 28 Pt 1: p. 279-328.

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